1. Field of the Invention
This Invention relates to automatic fastening machines or tools, and, in particular, to the fastener delivery head for such automatic fastening machines or tools.
2. Prior Art
Prior patent specifications, PCT/AU92/00621(WO 93/09918) and PCT/AU94/00013(WO 94/15736) by the present applicant both disclose automatic fastening machines or tools wherein the fastening head thereof operates with rivets and other types of fasteners, fed thereto in alignment with a punch or engagement tool therefor, and supporting the rivets or other fastener as the punch or engagement tool advances the rivet or other fastener towards a workpiece (and typically an upsetting die in the case of rivets).
While the fastening machines or tools disclosed in the above documents have found commercial acceptance, customers continue to propose new applications for fasteners, fastening diverse ranges of workpieces together, and particularly where access for the fastening operation is restricted, and sometimes extremely limited. The need to provide fastener aligning, centralising, and anti-tumbling features in the fastening head or nose pieces, particularly leading up to, and at the exit point thereof for a fastener, by reduced dimension of the parts, introduces fragility if the old techniques for control are retained. Short rivets in particular need to be controlled and the prior art has proposed steel balls or jaws for this purpose. If these are to be used they must be provided up to, and very close to, the front face or nose of the fastening apparatus to prevent tumbling, for example. A staggered sequence of such balls, or like type devices, over the length of a delivery tube requires a fairly elaborate construction, which restricts the capacity to reduce the front end dimensions of the fastener feeding head.
It is an object of the present invention to provide a fastening head which addresses the aforementioned disadvantage in front end dimension. Other objects and various advantages will hereinafter become apparent.
The invention achieves its object in provision of a fastener feeding head for a fastening machine or tool by which to apply fasteners to a workpiece, said fastening head including;
a guide means with a fastener passage there through;
a drive means mounted for advance and retraction in the fastener passage;
a fastener engagement means disposed in the fastener passage at or on a leading end of the drive means; and
a fastener feed means feeding fasteners to the fastener passage, operative to align fasteners in the fastener passage with the drive means;
characterised in that:
a gas control means is operative to effect or establish a gas pressure in the fastener passage which is operative to maintain a fastener therein in contact with, or in proper alignment or orientation to, the drive means as the drive means is advanced in the fastener guide passage. In order to effect the desired outcome the cross sectional dimension of the fastener passage is ideally closely fitted to the radial dimension of the fastener, its head in the case of a rivet. Alternately the foregoing might be achieved by careful dimensioning of the fastener engagement means such that it adequately fits to the fastener passage such that a suitable degree of pressurisation is developed and maintained in the fastener passage. A similar level of seal is required between the front end of the fastener passage and the work pieces as is will be more clearly developed herein below.
Preferably a fastener feeding head has a fastener feed means which includes a delivery passage for fasteners, fitted with a compressed gas source, operative to propel fasteners there through to the fastener passage, there being a gate means associated with the guide means to selectively isolate the fastener passage from the delivery passage. The fastener feeding head is ideally associated with a gas flow means in or associated with the guide means selectively directs gas from the delivery passage to the front or nose end of the fastener passage, forwardly spaced from the drive means, to cause compressed gas to maintain fasteners in contact with the drive means as the drive means is advanced in the fastener passage. Preferably a fastener feeding head in accordance with the invention is one wherein the gas flow means includes a piston driven gate means to switch gas in the delivery passage to flow passages leading to the front or nose end of the fastener passage.
Preferably a fastener feeding head in accordance with the invention is one wherein one or more balls or the like are retractably mounted in the guide means to retractably extend into the fastener passage, on the opposite side thereof to the junction between the delivery passage and the fastener passage, to assist alignment or centralising of the fasteners with the punch. Ideally a fastener feeding head is one wherein fasteners are supplied to the delivery passage by a supply tube which may have an internal profile complementary to the shape of the fasteners, the fasteners being propelled by compressed air blown down the supply tube. Ideally there is provided a gate means which is pneumatically controlled and the flow passages include one or more ports directed into the fastener passage adjacent the nose end, the gas directed thereto being sufficient to maintain contact of a fastener with the fastener engagement means when the nose of the guide bush or feeder block engages with a workpiece.
Preferably a fastener feeding head in accordance with the invention is one wherein when the nose end of the guide means is in contact with a workpiece, a vacuum means selectively at least partially evacuates the fastener passage to maintain the fasteners in contact with the punch as the punch is advanced in the fastener guide passage. Ideally there is a compressed gas source to propel a fastener through the delivery passage to the fastener passage, a gate means to selectively isolate the fastener delivery passage from the fastener guide passage after delivery thereto of a fastener, and, when the nose end of the fastener passage is in contact with a workpiece, and a vacuum means to selectively, at least partially, evacuate the fastener passage to maintain the fastener in contact with the fastener engagement means as it is advanced in the fastener guide passage. Ideally there is at least one slot or groove provided in the nose end of the guide means to allow air to be drawn into the fastener passage when the nose end is in contact with a workpiece or at least one slot or groove is provided in the wall of the fastener passage, connected to at least one port, in turn connected to a vacuum source, wherein the vacuum source is operative to draw air into the fastener guide passage through one or more grooves or ports in the nose end of the guide means, air creating the means by which a fastener is maintained in contact with the fastener engagement means as it drives the fastener through the fastener passage into engagement with a workpiece.
Preferably the invention provides a fastener feeding head wherein the guide means is a guide bush, the drive means is a plunger mounted for coaxial advance and retraction through the guide bush, the fastener engagement means is a punch located at or on a leading end of the plunger, and a carrier tape means transports rivets to the fastener passage, and a gas passage or port means in the guide means operable to connect a supply of compressed gas to the nose end of the fastener passage to cause the compressed gas to be directed into the fastener guide passage, spaced from the punch, the compressed gas being operative, in use, to maintain the rivets in contact with the punch as the punch is advanced in the fastener passage. Ideally the gas control means includes means in the guide means operable to connect a supply of compressed gas to the nose end of the fastener passage the compressed gas being switchable to maintain the fasteners in contact with the fastener engagement means as needed. The compressed gas means and vacuum means may be selectively controlled by switchable or computer controlled valves.
Throughout the specification, the term xe2x80x9cfastenerxe2x80x9d shall include rivets, screws, and like type fastening devices, nuts, washers and similar type products with a ratio of radius to axial length calls for the handling capacity of the invention herein set forth. The preferred embodiments are in respect of rivets but the extension to other fasteners only requires a variation of the fastener engagement means used in the apparatus. Thus the punch of the preferred embodiments may be readily replaced by a driver for screws, in the case of screw fasteners as will be readily apparent to the man skilled in the art.